[cursor]

Fixes #

What and why

Nightly simplification of merges after #4795. Graph IANA fallback and fractional-second stripping live in one helper; Prefer UTC headers share one constant with the normalizer timezone. The duplicate exception-recurrence branch is gone, toRRule inlines the one-line wrapper, seriesWriteKey reuses seriesIdOf, and remainder-series stripRuleBounds sits next to truncateSeriesRulesBefore. No product behavior change.

Verify

Selected local checks passed: test:sync:fast, test:web, type-check, lint, knip, test:a11y.

test:e2e ran 294 passed, 3 failed under parallel load. Isolated retry:

• e2e/billing/signup-trial-step.spec.ts (awaiting checkout can explore...) passed
• e2e/calendars/calendar-experience.spec.ts (holiday all-day dedupe) and e2e/calendars/cross-provider-duplicates.spec.ts still fail because the fixtures stamp UTC today (2026-10-25) while the Denver week grid is still Sat 2026-10-24 (visible week Oct 18-24). The diff does not touch week windowing, holiday dedupe, or duplicate merge. Sandbox date-boundary flake; CI decides.

VERDICT: FAIL
Failed: test:e2e

  

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Note

Low Risk
Refactor and deduplication across Microsoft sync and optimistic recurrence helpers; intended no product behavior change, with narrow recurrence-mapping guard removal as the only subtle touchpoint.

Overview
Consolidates Microsoft Graph timezone and HTTP concerns: graphTimeZoneToIana and stripGraphDateTimeFraction move into microsoft-graph-timezone, Graph Prefer: outlook.timezone strings centralize in microsoft-http.constants, and readers/writers/normalizers/cancelled-occurrence mapping call those shared pieces instead of duplicating logic.

On calendar-web, seriesWriteKey derives the master id via seriesIdOf, stripRuleBounds lives beside truncateSeriesRulesBefore (with a unit test), and several optimistic-mutation helpers are module-private only. mapRecurrence drops the redundant type === "exception" guard before the seriesMasterId / originalStart instance path, and toRRule inlines a one-line pattern normalizer wrapper.

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[github-actions]

Boot bundle: 527.3 KB gzip (+0.0 KB vs main)

[tyler-dane]

agent-loop: still conflicting after update-branch onto main. Closing so the issue can be relaunched.